The U.S. Court of Appeals for the Ninth Circuit has been charged with deciding if proponents of the anti-gay marriage Proposition 8 in California have standing to appeal a U.S. District Court ruling that Proposition 8 is unconstitutional. Officials from the State of California, who agree with the trial court, have refused to do so.
The 9th Circuit has dealt with this issue by asking the California Supreme Court in what is called a "certified question" if proponents of a ballot initiative have standing to defend it under state law, which would confer the right to bring an appeal even in the absence of a federal law basis for doing so.
In practice, it is extremely likely given the prior litigation history of the case and recent relevant California Supreme Court rulings, that the California Supreme Court will find that the proponents have standing to appeal under state law. Thus, the trial court ruling holding that Proposition 8 is unconstitutional will remain in force and gay marriage will very likely resume in California.
In theory, the federal standing issue could be appealed to the U.S. Supreme Court, which could grant certiorari to review it (or possibly consider it as a request for a writ of mandamus, another form of appeal in a situation where the name of the kind of appeal taken doesn't matter much). But, because the key issue pertains to the rights conveyed by state law under a state initiative process, and the prior federal precedents on that issue are fairly clear, the U.S. Supreme Court is unlikely to do so, and would be bound by any California Supreme Court determination of state law issues in any case.
If the California Supreme Court rules that the ballot issue supporters lack standing, as I predict that it will, there will be a ruling in force that effectively legalizes gay marriage in California via federal court order, but because no decision on the merits has been made at the 9th Circuit or U.S. Supreme Court level, the precedent will have no effect outside the State of California.